Process for the preparation of non-woven fabrics

ABSTRACT

NON-WOVEN FABRICS HAVING EXCELLENT SOFTNESS AND FLEXURAL RESISTANCE ARE PREPARED BY APPLYING AN AQUEOUS SOLUTION OF AT LEAST ONE WATER-SOLUBLE, HIGH MOLECULAR SUBSTANCE TO A FIBROUS WEB, DRYING THE SAME APPLYING TO THE DRIED WEB A BINDER SOLUTION COMPOSED OF AT LEAST ONE BINDER DISSOLVED IN A SOLVENT WHICH IS A NON-SOLVENT TO THE FIBERS CONSTITUTING THE FIBROUS WEB AS WELL AS TO THE WATER-SOLUBLE, HIGH MOLECULAR SUBSTANCE, SOLIDIFYING THE BINDER SOLUTION THEREBY FIXING THE BINDER ON THE WEB, AND THEREAFTER DISSOLVING AND REMOVING THE WATER-SOLUBLE, HIGH MOLECULAR SUBSTANCE FROM THE WEB.

u 1 TOSHIKAZU SHINOHARA L 3,539,930

PROCESS FOR THE PREPARATION OF NON-WOVEN FABRICS Filed June 24, 1968 2 Sheets-Sheet I TOSHmAZu SHINDHARA.

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June 1971 TOSHIKAZU SHINOHARA E 3,539,930

PROCESS FOR THE PREPARATION OF NON-WOVEN mazucs Filed June 24. 1968 2 Sheetsheet 2 lOO FLEXURAL RIGlDlTY (q) PVA PICK-UP (/o) TOSHIKAIU SHINOHARA. HIROSHI HATTODJ AND MAKOTD KOUNDSU,

INVIJN'I'ORS United States Patent 3,589,930 PROCESS FOR THE PREPARATION OF NON-WOVEN FABRICS Toshikazu Shinohara, Hiroshi Hattori, and Makoto Kounosu, Ohtsn-shi, Japan, assignors to Toray Industries, Inc., Tokyo, Japan Filed June 24, 1968, Ser. No. 739,556 Claims priority, application Japan, June 27, 1967, 42/40,723 Int. Cl. B4411 1/44 US. Cl. 117-63 9 Claims ABSTRACT OF THE DISCLOSURE Non-woven fabrics having excellent softness and flexural resistance are prepared by applying an aqueous solution of at least one water-soluble, high molecular substance to a fibrous web, drying the same applying to the dried web a binder solution composed of at least one binder dissolved in a solvent which is a non-solvent to the fibers constituting the fibrous web as well as to the water-soluble, high molecular substance, solidifying the binder solution thereby fixing the binder on the web, and thereafter dissolving and removing the water-soluble, high molecular substance from the web.

This invention relates to a process for the preparation of non-woven fabrics of excellent softness and flexural resistance.

More particularly, the invention relates to a process for the preparation of non-woven fabrics which comprises applying an aqueous solution of at least one water-soluble, high molecular substance to fibrous Webs, drying the same, further applying thereto a binder solution composed of at least one binder dissolved in a solvent which is a non-solvent to the fibers forming the webs as well as to the water-soluble high molecular substances, fixing the binder on the webs by drying or coagulation in a coagulant bath, and thereafter dissolving and extracting the Water-soluble, high molecular substance or substances from the webs, with water of normal or slightly elevated temperature.

Numbers of proposals have been made concerning preparation of non-woven fabrics, but the conventional products are almost invariably inferior in such properties as softness and flex life. This is because, in the conventional products, the mobility of the constituent fibers is restricted when the non-woven fabrics are deformed, by the binder which is intimately adhered to the fibers. This intimate adhesion of the fibers with the binder also causes exertion of excessive stress on the non-woven fabrics, or on the points of their adhesion during the flexural deformation, which obviously deteriorates the fiexural resistance of the product. Whereas, the present invention is now completed as the results of our many years of laborous research works in the purpose of improving these deficiencies.

The invention can be more tangibly explained with reference to the attached drawings. FIG. 1 is an enlarged cross-section of the fiber composing the non-woven fabric obtained in one of the working examples of this invention. FIG. 2 shows an enlarged cross-section of the fiber constituting a conventional non-woven fabric.

In the FIG. 1 and FIG. 2 of the drawings, 1 is the constituent fibers of non-woven fabrics, 2 is the binder, and 3 denotes the voids formed by the removal of watersoluble, high molecular substance.

From FIG. 1, it can be understood that while the non- Woven fabric of the invention is composed of the constituent fibers and binder, voids are formed therebetween by the removal of water-soluble, high molecular substance. In contrast thereto, in the conventional non-woven fabrics the constituent fibers are directly adhered with the binder, leaving no space therebetween.

Thus, because the fibers and binder are not intimately adhered in the non-woven fabrics prepared in accordance with the invention, the fibers can be freely shifted with the deformation of fabric. This contributes to the excellent softness or suppleness of the fabric. The fabric also exhibits a very long flex life, since during the bending deformation, the deformation stress is received by the binder of low modulus which is not adhered with the fibers. This markedly alleviates the stress on the fibers.

The above-described effects are not found in the conventional non-woven fabrics, because in those products the fibers are directly bonded with the binder.

Any type of fibers which have been used in conventional non-woven fabrics can be employed as the constituents of the fibrous webs in accordance with the invention. For example, cotton, hemp, wool, rayon, acetate, nylon, polyester fibers, polyacrylic fibers, vinyl fibers, polyolefin fibers, mixtures of the foregoing, etc., can be used.

The webs are formed by means of known devices for making non-woven fabrics, such as card, cross -lappers, random webbers and paper machines. Plural webs may be superposed and integrated by needle punching or stitching. Also felt is included within the scope of fibrous Web of this invention.

As the water-soluble, high molecular substance with which the fibrous Webs are to be treated, polyvinyl alcohol, CMC (carboxymethyl cellulose), casein, polyvinyl methyl ether, starch, and the like are suitable. Thosecompounds are used in the form of aqueous solution. The application of any of those compounds to the webs is achieved by spraying the aqueous solution onto the webs, or by impregnating or coating the latter with the former. The webs are then dried.

The pick-up of the water-soluble, high molecular substance preferably ranges approximately 2 to 50% to the Weight of the web, but the pick-up may be varied beyond the above range, if necessary.

When the pick-up of the water-soluble, high molecular substance is less than approximately 2%, hardly any void is formed between the constituent fibers of the nonwoven fabric and the binder, and the effects of the invention, i.e., excellent softness and fiexural resistance, are not obtained.

Whereas, when the pick-up exceeds 50%, the binder which is applied to the web in the next step can hardly permeate into the fibrous Web, but tends to stay on the surfaces thereof. This renders the extractive removal of the water-soluble, high molecular substance difiicult, and furthermore prevents the uniform application of binder onto the web.

In the next step, the fibrous web which has been treated with the water-soluble, high molecular substance is further treated with a binder solution. The solution is formed by dissolving a binder in a solvent which is a non-solvent to the constituent fibers of the non-woven fabric as well as to the water-soluble, high molecular substance. The binder may be any of those which are conventionally used for the preparation of non-woven fabrics, such as natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylatebutadiene copolymer, polyurethane, other synthetic rubber, and mixtures of the foregoing.

As the solvent, any known solvent is usable so far as it is a non-solvent to the above water-soluble, high molecular substances and fibers but is a good solvent to the binder.

In order to secure uniform adhesion of the binder to the non-woven fabric, however, solvents of better miscibility with water are preferred. As such solvents, for example, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, tetramethylurea, dimethylacetamide, -N-methyl-2-pyrrolidone and dioxane may be named.

Thus, a few examples of the combination of fibers constituting the webs, water-soluble high molecular substance, solvent of the binder, and binder will be as follows: polyamide fibers-polyvinyl alcohol-dimethylsulfoxide-polyurethane; polyester fibers-carboxymethyl cellulose-dimethylformamide-polyurethane; cellulosic fibers-polyvinyl alcohol-dimethylformamide-polyurethane. It should be understood that the above examples of combination are given strictly for illustrative purpose, but by no means in restrictive sense.

The binder solution is applied to the fibrous web which has been treated by the water-soluble, high molecular substance, by spraying, impregnation or coating. The web is then either dried so that the binder may be fixed, or immersed in water to cause solidification of the binder. Thus, the solvent is removed from the binder, and the binder is dried and set.

The binder pick-up is variable over a wide range depending on the characteristics required of specific usage of the product. Normally preferred range is 15 to 150% to the Weight of the fibrous web.

When the binder pick-up is less than 15%, the bonding of the constituent fibers is weak, and the strength of the product non-woven fabric is unsatisfactory. Whereas, when it exceeds 150%, the subsequent dissolution and removal of the water-soluble, high molecular substance becomes hardly operable.

The web to which the binder has been adhered and set is removed of the water-soluble, high molecular substance by means of water of preferably slightly elevated temperature. The removal can of course be achieved with other solvents, such as alcohol, etc. Also complete removal is not necessarily required. By suitably controlling the quantity of removal of the water-soluble, high molecular substance, the softness of the product can be optionally selected.

Thus obtained non-woven fabrics can be further subjected to optional treatments or processing depending on the intended usage, for example, coating, slicing, bufling, embossing dyeing, staking, pressing and lamination, etc.

The non-woven fabrics obtained in accordance with the invention are markedly softer than the conventional products, and furthermore exhibited a long flex life.

The invention now will be explained in greater details by means of working examples, in which percentages are by weight unless otherwise specified.

EXAMPLE 1 Nylon staple fibers of 5 d. x 76 mm. dimensions were formed into a web weighing about 250 g./m. with a random webber. The web was treated with aqueous solution of polyvinyl alcohol. The solid pick-up was 40% to the weight of the fibrous web. The web was then dried at 110 C. for 25 minutes.

Thus dried web was treated with a dimethylformamide (DMF) solution of NBR (acrylonitrile-butadiene copolymer rubber), with a solid pick-up of 130% to the Weight of the fibrous web. Immediately thereafter the web was immersed in water of C. so as to solidify NBR and remove DMF, followed by another immersion in 95 C. water to be thoroughly extracted of the first applied polyvinyl alcohol. The web was then dried at 105 C. for minutes. The resultant product was a very soft nonwoven fabric, which exhibited excellent flex life.

As a control, the above web (felt) was first treated with 15% DMF solution of NBR with a solid pick-up of 130% to the weight of the web, and immediately thereafter immersed in 25 C. water so as to solidify NBR and remove DMF. Thus a conventional non-woven fabric was obtained.

The comparative data on the properties of the product of this example with those of the control product are given in Table 1 below.

1 Gurlery softness was measured with a Gurlery's softness tester.

2 The flexural resistance was measured with a Nikka-type flex life tester. Repetitive bendiugs were given to the test samples at -5 C., and the number of bendings were counted until the samples were broken. (Measurement method by Nikka-type blending tester: A test piece with a size of 4 x 5 cm. is bent, and mounted onto a flex life tester with a seizing interval of 3 cm. It is bent with a transfer distance of 2 cm. and at a rate of 250 times per minute. The number of bending operations when the test piece undergoes the first cracking is measured.)

From the above Table 1, it is apparent that the nonwoven fabric prepared in accordance with the invention excels over the conventional product in softness and flexural resistance.

EXAMPLE 2 Polyester staple fibers of 1.5 d. x 38 mm. dimensions were formed into a web of approximately 300 g./m. by means of a cross-lapper, which was then converted to a felt having a needling density of 750/cm. by needlepunching. The felt was treated with 5% aqueous solution of CMC to a solid pick-up of 35% to the weight of the felt, and dried at 110 C. for 30 minutes.

Then the felt was treated with a 20% DMF solution of polyurethane to a solid pick-up of to the Weight of the felt, and immediately thereafter immersed in 25 C. water. Whereupon the polyurethane was solidified and DMF was removed. The felt was then immersed in 95 C. water to be thoroughly extracted of CMC, followed by drying at C. for 40 minutes.

The resultant product was a very soft non-woven fabric which exhibited excellent flex life.

EXAMPLE 3 The same Web employed in Example 1 was applied with polyvinyl alcohol (molecular weight: 500, degree of acetylation: 13 mol percent) to a solid pick-up of 10% to the weight of the fibrous web. Then the web was treated with 15% DMF solution of polyurethane to a solid pick-up of 30%, followed by drying with a drying oven of 80 C. Whereupon DMF was volatilized and polyurethane was fixed on the fibers. The resultant sheetformed product was immersed in hot water of 80 C. to cause dissolution of the polyvinyl alcohol, and thereafter dried in a drying oven of C. for 30 minutes.

Thus obtained non-woven fabric was soft, had high strength and furthermore exhibited favorable properties similarly to the product of Example 1.

EXAMPLE 4 The same felt employed in Example 2 was treated with polyvinylpyrrolidone to a solid pick-up of 20%, and then with 20% DMF solution of polyurethane to a solid pickup of 50% to the weight of the fibrous felt. Thereafter the felt'was immediately thrown into water to be removed of the solvent, and the polyurethane was set in situ, followed by complete removal of polyvinylpyrrolidone in warm water of 60 C. The product was then dried to provide soft and tough artificial leather.

The result was quite satisfactory similarly to the result of Example 2.

EXAMPLE 5 The same felt employed in Example 2 was applied with 5 parts of CMC per 100 parts by weight of the fibrous felt, and thereafter treated with a solution of polyamide in a methanol solution of calcium chloride to a solid pick-up of 30% to the fibers. The felt was then immersed in water so as to be removed of the solvent,

and polyamide was fixed in situ. Thereafter CMC was removed from the felt in warm Water of 60 C. Thus soft and touch non-woven fabric was obtained.

The result was quite satisfactory similarly to the result of Example 2.

EXAMPLE 6 175 parts of nylon staple fibers of 3 d. x 51 mm. dimensions and 75 parts of polyester staple fibers of same dimensions were mixed 'and formed into a web of 250 g./m. by means of a cross-lapper. The web was converted to a felt having a bulk density of 0.12 g./cm. by needle-punching. The felt was immersed in aqueous solutions of polyvinyl alcohol of various concentrations, squeezed, and dried.

Thus obtained samples of different polyvinyl alcohol pick-ups were then treated with DMF solution of polyurethane to each polyurethane solid pick-up of parts (per 100 parts of fibrous felt). The polyurethane was solidified in situ in 25 C. water, and DMF as well as polyvinyl alcohol were removed from the felt by prolonged washing with 80 C. water. The samples were then dried at 120 C.

From each of thus obtained non-woven fabrics, a test piece of 5 cm. x 2 cm. was cut, and flexural rigidity of the test piece was measured as follows: each sample was held at its two ends with a span length of 1 cm., and a load was exerted concentratively at the center of the sample. The flexural rigidity was expressed by the Weight of the load at which the flexion of the sample reached 20% of the span length. The correlation between the polyvinyl alcohol (PVA) pick-up (percent) on the samples and their flexural rigidity g drew a curve as in the FIG. 3.

Less flexural rigidity g of the sample denotes greater softness. Thus, it can be understood from the graph above that the PVA-treated non-woven fabrics possess markedly greater softness over the untreated sample (in the graph, the sample of zero PVA pick-up).

EXAMPLES 7-11 AND CONTROLS 1-6 From the same web as employed in Example 1, non- Woven fabrics were prepared under various treating conditions as indicated in Table 2 below. The properties of the products are also given in the same table.

TABLE 2 Treating conditions Properties of product Polyurethane pick-up (percent) Intensity PVA of pick-up (percent) Flexural rigidity g breakage (kg/em.)

11 Control 6 50 From the data above, it can be understood that when the binder pick-up is less than 15% as in the case of Control 1, the strength is too low for practical use. Whereas, the sample of a binder pick-up greater than 150% (Control 6) still lacked softness even when its PVA pick-up was raised to the upper limit. Thus it is clear that the suitable binder pick-up ranges from 15 to 150%. The samples of Controls 2-5 exhibited poor softness.

Also at the PVA pick-up of 2%, other treating conditions can be varied over a wide range, still yielding products of satisfactory strength and softness. However the range is markedly narrow at the PVA pick-up of 6 above 50%. This denotes more difficult handling in the latter case.

We claim:

1. A process for the preparation of non-woven fabrics having increased softness and flexural resistance which comprises impregnating a fibrous web with an aqueous solution of at least one water-soluble, solid high molecular substance, drying the same, impregnating the dried web with a binder solution composed of at least one binder dissolved in a solvent which is a non-solvent to the fibers constituting the fibrous web as well as to the water-soluble, solid high molecular substance, the pick-up of solid high molecular substance and binder being about 250% and 15150%, respectively, by weight of the fibrous web, fixing the binder on the web by means of solidification and thereafter dissolving and removing the water-soluble, high molecular substance from the web, providing substantially continuous void between said fibers and the binder.

2. The process according to claim 1, wherein the fibrous web consists essentially of polyamide fibers.

3. The process according to claim 1, wherein the fibrous web consists essentially of polyester fibers.

4. The process according to claim 1, wherein the fibrous web consists essentially of a mixture of polyamide fibers and polyester fibers.

5. The process according to claim 1, wherein solidification of the binder is carried out by means of drying the binder.

6. The process according to claim 1, wherein solidification of the binder is carried out by means of coagulating the binder.

7. The process of claim 2 in which the water-soluble, high molecular substance is at least one compound selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, casein, polyvinyl methyl ether, and starch, and the binder is at least one compound selected from the group consisting of natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, polyurethane and mixtures thereof.

8. The process of claim 3 in which the water-soluble, high molecular substance is at least one compound selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, casein, polyvinyl methyl ether, and starch, and the binder is at least one compound selected from the group consisting of natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, polyurethane, and mixtures of the foregoing.

9. The process of claim 4 in which the water-soluble, high molecular substance is at least one compound selected from the group consisting of polyvinyl alcohol, carboxymethyl cellulose, casein, polyvinyl methyl ether and starch, and the binder is at least one compound selected from the group consisting of natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, polyurethane, and mixtures of the foregoing.

References Cited UNITED STATES PATENTS 1,713,679 5/1929 Snelling ll763 2,727,278 12/1955 Thompson 11763X 2,969,791 1/ 1961 Ekenstam 117--63X 3,121,698 2/1964 Orsino 117--143 2,673,825 3/1954 Biefeld 117-135.5X

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R. 

